Mooseman
Moderator
You sure it's the ECT? I had the same thing happen to me halfway to DC and the ECT was loose. Tightened it up and was good to go. You did use the aluminum sealing washer? Maybe the seal around the t-stat is leaking or it's loose.
Oblong? Maybe the washer is borked? It should have been round. Maybe replace it with a copper washer unless you can find an aluminum one.
Have you checked the fan clutch? If it seems to just freewheel all the time, it may be dead, especially with the A/C on and running hotter than usual.
How to test the electro-viscous fan clutch
Edit: forgot to mention...while I held the Fan I could feel like a light thumping in the assembly as if someone was hit the Fan while holding it. Is this the resistance I was looking for?
That's the pulse signal of the clutch engaging, to get the fan to spin.
So since I can rule out the Fan Clutch...what do you guys suggest I should look into next?...
1. Possible weak Water Pump?
2. Wrong mix of Coolant?
3. Restricted Coolant flow/circulation?
4. Defective (new) T-Stat?
Also, with outside temperatures around 100F Degrees and AC On...what should the highest Coolant Temperature reading be for this Engine?...never over 210F?
Fan will engage more as the temp goes up. It will be really going if it were to get near the halfway to overheat.
I'd say it's normal to run a little warmer on hot days with A/C on but just slightly to the right of 210. Fan will engage more as the temp goes up. It will be really going if it were to get near the halfway to overheat. Just make sure your condenser and radiator are clear of bugs and dirt.
It is quite possible you have a defective new t-stat. It has happened before and IIRC, it was even an ACDelco. It happens. Maybe we should start testing them in boiling water before installing them.
Coolant mix in your part of the continent should be 50/50 for better heat transfer performance. You could also add some Water Wetter, which does help in heat transfer. I have used it in my snowmobile and have noticed a difference. Can't hurt to try it.
GM went cheap on the radiator putting in one that was barely adequate, hence the reason they went overboard with the clutch fan (and no efans like the other trucks).
The Temperature Guage has been going slightly over the 210F mark, almost one tick to the right of 210F. But only when outside temperatures are around 90-100F and with the AC On. All other occasions it has been sitting right on 210F, like it should.
That is normal as the cooled coolant flows from top to bottom. It's a reverse flow system.
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Ok since I changed mine out too, the 210F mark is where mine is at around the 90-100F mark as well, drove in 107F with the AC on...it went maybe 1 mark to the right of 210F and stayed there. Now that I know this normal, the TB is at operating temps now. I wouldn't worry too much about this...